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Thermal Activation of Methane and Ethene by Bare MO .+ (M=Ge, Sn, and Pb): A Combined Theoretical/Experimental Study
Author(s) -
Chen Kai,
Wang ZheChen,
Schlangen Maria,
Wu YunDong,
Zhang Xinhao,
Schwarz Helmut
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101538
Subject(s) - chemistry , hydrogen atom abstraction , dissociation (chemistry) , bond dissociation energy , metal , density functional theory , hydrogen , hydrogen atom , oxide , atom (system on chip) , molecule , methane , photochemistry , inorganic chemistry , computational chemistry , organic chemistry , alkyl , computer science , embedded system
The thermal ion/molecule reactions (IMRs) of the Group 14 metal oxide radical cations MO . + (M=Ge, Sn, Pb) with methane and ethene were investigated. For the MO . + /CH 4 couples abstraction of a hydrogen atom to form MOH + and a methyl radical constitutes the sole channel. The nearly barrier‐free process, combined with a large exothermicity as revealed by density functional theory (DFT) calculations, suggests a fast and efficient reaction in agreement with the experiment. For the IMR of MO . + with ethene, two competitive channels exist: hydrogen‐atom abstraction (HAA) from and oxygen‐atom transfer (OAT) to the organic substrate. The HAA channel, yielding C 2 H 3 . and MOH + predominates for the GeO . + /ethene system, while for SnO . + and PbO . + the major reaction observed corresponds to the OAT producing M + and C 2 H 4 O. The DFT‐derived potential‐energy surfaces are consistent with the experimental findings. The behavior of the metal oxide cations towards ethene can be explained in terms of the bond dissociation energies (BDEs) of MO + H and M + O, which define the hydrogen‐atom affinity of MO + and the oxophilicity of M + , respectively. Since the differences among the BDEs(MO + H) are rather small and the hydrogen‐atom affinities of the three radical cations MO . + exceed the BDE(CH 3 H) and BDE(C 2 H 3 H), hydrogen‐atom abstraction is possible thermochemically. In contrast, the BDEs(M + O) vary quite substantially; consequently, the OAT channel becomes energetically less favorable for GeO . + which exhibits the highest oxophilicity among these three group 14 metal ions.